The present invention relates generally to mass spectrometers, and particularly to a device and method for introducing a sample into a mass spectrometer which employs a semipermeable capillary tube.
The selected introduction of components of a fluid into a mass spectrometer has been a long standing problem. One approach to solving this problem has been the use of various types of molecular separators including membrane separators. The use of membrane separators is particularly advantageous when it is desired to monitor organics in an aqueous medium. These membrane separators have permitted trace solution analysis, gas analysis, and in vivo studies for low molecular weight organic molecules. They have also been applied to reaction monitoring, including the indirect analysis of particular components through secondary product formulation. The following publications and patents are exemplary of the state of the art in this field: "Novel Mass Spectromatric Sampling Device-Hollow Fiber Probe", by L. B. Westover, J. C. Tou, and J. H. Mark, Analytical Chemistry (1974), Volume 46, page 568; "Biochemical Assay By Immobilized Enzymes And A Mass Spectrometer", by J. C. Weaver, M. K. Mason, J. A. Jarrell, and J. W. Peterson, Biochimica et Biophysica Acta, (1976), Volume 438, page 296; "Mass Spectrometer Polymer Membrane Sample Introduction Device", by G. J. Kallos and N. H. Mahle, Analytical Chemistry (1983), Volume 55, page 813; Llewellyn, et al U.S. Pat. No. 3,429,105, issued on Feb. 25, 1969; Lucero U.S. Pat. No. 3,926,561, issued on Dec. 16, 1985; Kabler U.S. Pat. No. 3,638,401, issued on Feb. 1, 1972; Littlejohn U.S. Pat. No. 3,649,199, issued on Mar. 14, 1972; and Saunders U.S. Pat. No. 3,662,520, issued on Mar. 16, 1972.
In general, these prior membrane interfaces have been positioned exterior to the ion source of the mass spectrometer. This can cause condensation along the transfer lines which can result in poor response times, memory effects and analyte dilution for these otherwise useful configurations. In addition to the problems caused by the distance for which the analyte must travel to reach the ion source of the mass spectrometer, room temperature interfaces often give poor response times and memory effects due to the effect of lower permeation rates with temperature. Other shortcomings of the prior art include the reliance on relatively large sample volumes and the lack of the provision for the removal of excess or waste solution.
Accordingly, it is a principal objective of the present invention to provide a novel device for introducing a sample into a mass spectrometer which employs a semipermeable capillary membrane.
It is a more specific objective of the present invention to provide a mass spectrometer interface which employs a semipermeable capillary tube through which a fluid containing the sample to be analyzed is permitted to flow.
It is another objective of the present invention to provide a capillary membrane interface to a mass spectrometer which can be directly disposed in the ion source of the mass spectrometer.
It is a further objective of the present invention to provide a direct insertion membrane probe (DIMP) for the selective introduction of organic molecules from an aqueous solution into a mass spectrometer.
It is an additional objective of the present invention to provide a direct insertion membrane probe which does not require large sample volumes and also permits recycling of the aqueous solution through the capillary membrane.
It is yet a further objective of the present invention to provide a direct insertion membrane probe which can be used with a variety of mass spectrometers, including tandem mass spectrometers.
It is yet another objective of the present invention to provide a direct insertion membrane probe which is heated to enhance the analyte permeation rate and decrease any memory effects in the capillary membrane.
It is still an additional objective of the present invention to provide a direct insertion membrane probe which may be used to monitor samples from a reaction process.
It is still a further objective of the present invention to provide a direct insertion membrane probe which is economical to manufacture and which displays high sensitivity, especially for components in aqueous solutions.